The present invention comprises a new and distinct cultivar of calla lily, botanically known as Zantedeschia sprengeri and hereinafter referred to by the cultivar name ‘Monte Carlo’.
‘Monte Carlo’ is a product of a planned breeding program which had the objective of creating Zantedeschia hybrids for pot flower production in a wide range of colors with a large, classic flower shape. The breeding program began in 1989, and the new cultivar is a seedling selected from the crossing of a Zantedeschia sprengeri selection referred to as Z010161 (female parent, unpatented) with a Zantedeschia sprengeri selection referred to as Z030217 (male parent, unpatented). ‘Monte Carlo’ was selected in 2012 by the inventor in 't Zand, The Netherlands as one flowering plant within the progeny of the stated cross.
The first act of asexual reproduction of ‘Monte Carlo’ by tissue culture was performed by the inventor in September of 2012 in 't Zand, The Netherlands. Subsequent asexual reproductions by tissue culture at the same location have demonstrated that the combination of characteristics as herein disclosed for the new cultivar are retained and reproduced true to type through successive generations of asexual reproduction.
The following observations, measurements and comparisons describe plants grown in 18-20 cm pots at 12-14 weeks after planting in 't Zand, The Netherlands under greenhouse conditions, which approximate those generally used in horticultural practice. Color references are made to The 2001 R.H.S. Colour Chart of The Royal Horticultural Society of London, except where general color terms of ordinary significance are used.
The present invention has not been evaluated under all possible environmental conditions. The phenotype may vary with variations in environment without a change in the genotype of the plant.
The following traits have been repeatedly observed and determined to be basic characteristics of ‘Monte Carlo’ which, in combination, distinguish this calla lily as a new and distinct cultivar:                1. Yellow-colored spathes;        2. Compact plant architecture;        3. High inflorescence production; and        4. Lanceolate-shaped leaves.        
Further, when compared to calla lily plant named ‘Yellow Jacket BLZ’ (U.S. Plant Pat. No. 20,217), the upper surface spathe color of ‘Yellow Jacket BLZ’ is Yellow Group RHS 7A and the lower surface spathe color of ‘Yellow Jacket BLZ’ is Yellow Group RHS 7B, whereas the upper surface spathe color of ‘Monte Carlo’ varies between Yellow Group RHS 9A to 12A and the lower surface spathe color of ‘Monte Carlo’ varies between Yellow Group RHS 6A to 12A.
Table 1 provides differences of ‘Monte Carlo’ to its parents, Zantedeschia sprengeri selections Z010161 and Z030217.
TABLE 1‘Monte Carlo’DifferencesZ010161Spathe colorVaries between White Group RHSN155C to Red-Purple Group RHS62DPlant height25-50 cmZ030217Spathe colorVaries between Green-YellowGroup RHS 1C to Yellow GroupRHS 3APlant height20-35 cm